Jest setup: Stop polyfilling Promise.

It looks like this line was introduced in 3ff3987, in 2015, and it
has remained in a similar form since then. I haven't found any
explanation for it.

At jestjs/jest#10221 [1], a core Jest maintainer says,

"""
As an aside, one should never replace `global.Promise` [...]. E.g.
when using `async-await` you will always get the native `Promise`
regardless of the value of `global.Promise`.
"""

jestjs/jest#10221 is one issue this line has raised, for anyone
using the latest features of Jest to test async code in their React
Native projects.

[1] jestjs/jest#10221 (comment)

Fixes: facebook#29303

android/com/facebook/react/react-native/maven-metadata.xml

@@ -7,6 +7,6 @@
     <versions>
       <version>0.61.5</version>
     </versions>
-    <lastUpdated>20200825180753</lastUpdated>
+    <lastUpdated>20200825182101</lastUpdated>
   </versioning>
 </metadata>

android/com/facebook/react/react-native/maven-metadata.xml.md5

@@ -1 +1 @@
-aa57f1b2f064dca23b4b122f2715a941
+1f448be785da145276a61b82175013d2

android/com/facebook/react/react-native/maven-metadata.xml.sha1

@@ -1 +1 @@
-3a98ee4afadae726bc5c9805698318f8897bbfca
+070de441ae93253fc1f611eb8048757028197644

jest/setup.js

@@ -17,7 +17,6 @@ jest.requireActual('../Libraries/polyfills/error-guard');
 
 global.__DEV__ = true;
 
-global.Promise = jest.requireActual('promise');
 global.regeneratorRuntime = jest.requireActual('regenerator-runtime/runtime');
 
 global.requestAnimationFrame = function(callback) {